On Thu, Feb 2, 2012 at 17:24, gouarin <loic.gouarin at math.u-psud.fr> wrote:
> No. In those examples, you have the same grid for the velocity and the > pressure. If I use 4Q1_Q1 elements, I have not the same grid. I have one > for the velocity and an other for the pressure in the DMComposite. And for > me, it is the difficulty because as you say after, I have to do my own > preallocation step to have the good off-diagonal blocks. > Okay, I misinterpreted your notation. For your mixed elements, you would couple with DMComposite. > > This is why I asked what is the best way to construct my matrix. I hoped > that now it is not necessary to do this preallocation. > As long as dynamic preallocation is slow, you need to provide it. > This is also a difficulty to use a multigrid only on the velocity. > What is hard about using multigrid only on velocity? -pc_type fieldsplit -fieldsplit_velocity_pc_type mg -fieldsplit_velocity_pc_mg_levels 3 will do geometric MG on the velocity block. Note that your elements are slightly non-standard, so depending on how you want to work, you might provide your own coarsening and interpolation. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120202/95f77f9d/attachment.htm>
